1. Field of the Invention
The present invention provides a method and apparatus for continuous separation of proteins. More particularly, the invention involves the separation of proteins or protein fractions based on the difference in their isoelectric points. The method is easily carried out using an apparatus such as the hollow fiber membrane apparatus described herein.
2. Description of Related Art
A number of systems to separate proteins using electric fields have been described in the literature. These systems range from analytical devices to large scale (i.e. preparative) continuous purification systems. A number of common problems are shared by these electrophoretic systems. One problem is the convection due to heat generated by the electrolysis. Another problem is that electrophoretic systems separate all components of the input mixture making the separation more tedious, complex and expensive than necessary since usually only one component of the protein mixture is the desired product.
In analytical systems some type of anticonvective medium is typically used. For example, polyacrylamide gel, sucrose gradient or a bed of packed beads provide the anti-convective medium in many systems. The polyacrylamide gel system has the additional advantage that the gel acts not only as the convective stabilizer but also increases resolution by a sieving effect. The major limitations of these analytical systems are that they are not practical to scale up and are typically single use devices since the gels cannot be reused, typically, due to the configuration of such devices.
Some currently used means of stabilizing against convection in large scale systems are to operate under zero gravity (i.e. in earth orbit) or to produce a laminar flow field between two rotating cylinders (CTB Developments Limited, England). Amongst the major disadvantages of these systems are that they require complicated and costly devices and/or special environments to perform the separation.